Transcoding MPEG bittstreams for adding sub-picture content

Abstract

A DVD transport stream including a video and a sub-picture stream shall be transcoded to a broadcasting transport stream. For this a decoding-encoding-chain merging video and sub-picture into a single video bitstream to conserve the information of the sub-pictures although not in the broadcasting format reserved is provided. By performing a sub-picture macroblock analysis the transcoding can be controlled such that the motion estimation unit of a standard MPEG-2 encoder and/or the entire decoding loop within the encoder can be saved.

The invention claimed is: 
     
       1. Method for transcoding a picture data signal that includes a video bitstream and a DVD sub-picture bitstream into a single video bitstream, the method comprising, digitally decoding said DVD sub-picture bitstream into a DVD sub-picture signal, extracting from the DVD sub-picture signal a macroblock mask containing as affected macroblocks all those macroblocks that will be affected by the DVD sub-picture, generating, only in the affected macroblocks, newly encoded video data by decoding the video bitstream into a video signal, adding the video signal and the DVD sub-picture signal into a merged signal, and re-encoding the merged signal using intra macroblock type or zero vector prediction macroblock type, and generating a single video bitstream including unaltered encoded video data from the video bitstream in macroblocks other than the affected macroblocks, and including the re-encoded merged signal in the affected macroblocks. 
     
     
       2. Method according to  claim 1 , wherein the merged bitstream is a MPEG2 transport stream and the transport packets are delivered in bus packets over a bus connection of a home network to a device being equipped with MPEG2 decoder. 
     
     
       3. Method according to  claim 2 , wherein the bus of the home network is the IEEE1394 bus. 
     
     
       4. Device for transcoding a picture data signal that includes a video bitstream and a DVD sub-picture bitstream into a single video bitstream, the device comprising first and second decoders for digitally decoding said video bitstream and said DVD sub-picture bitstream into a video signal and a DVD sub-picture signal, respectively; a sub-picture macroblock analysis for generating a macroblock mask containing as affected macroblocks all those macroblocks that will be affected by the DVD sub-picture; an adder for merging, in the affected macroblocks, the video signal and the DVD sub-picture signal, an encoder for digitally encoding, in the affected macroblocks, said merged video and DVD sub-picture signals using intra macroblock type or zero vector prediction macroblock type, and a controller for generating said single video bitstream by including unaltered encoded video data from said video bitstream in macroblocks other than said affected macroblocks and including the re-encoded merged signal in said affected macroblocks. 
     
     
       5. Device according to  claim 4 , wherein the merged bitstream is a MPEG2 transport stream and the device comprises means for delivering the MPEG2 transport packets in bus packets for a bus connection of a home network. 
     
     
       6. Device according to  claim 5 , wherein the means for delivering the MPEG2 transport packets in bus packets are included in a IEEE1394 bus interface.